The culture war is back – and so is Rick Santorum.

The two developments may not be coincidental. Mr. Santorum – who clobbered Mitt Romney in all three Republican nominating contests Tuesday – is the biggest culture warrior in the 2012 presidential race. And the most incendiary social issues have lately come roaring back, with the church-state clash over birth control, funding for Planned Parenthood, and gay marriage all making headlines.

Another factor was likely at play in Tuesday’s stunning result: Mr. Romney, still the front-runner for the GOP nomination, didn’t try very hard. After all, the Minnesota caucuses, Colorado caucuses, and Missouri primary were just “beauty contests.” No delegates were awarded. Romney and the biggest "super PAC" that backs him did not spend much on advertising in any of those states. And he didn’t log the hours on the ground wooing voters that Santorum did.

But even straw polls have consequences, and now Romney may be kicking himself: In a shocker, Santorum won all three states, two by big margins, giving the former senator from Pennsylvania a sudden burst of momentum. In Minnesota, with 89 percent of results in, Santorum took 45 percent, Romney 27 percent, Newt Gingrich 17 percent, and Ron Paul 11 percent. Four years ago, Romney trounced eventual GOP nominee John McCain in Minnesota, 41 to 22 percent.

In Missouri, with 99 percent reporting, Santorum won 55 percent, Romney got 25 percent, and Mr. Paul got 12 percent. (Mr. Gingrich did not qualify for the ballot.)

In Colorado, Santorum’s margin of victory was the narrowest. With 99 percent reporting, he beat Romney 40 percent to 35 percent. Gingrich got 13 percent, Paul 12. But Colorado, where Romney was well-organized, was the biggest surprise of the night. Polling on caucus-eve had Romney ahead by double digits. Four years ago, Romney killed in Colorado, winning 60 percent of the vote to Senator McCain’s 18.

Maybe, in a way, Romney consoles himself with the knowledge that he won two of Tuesday’s three states in 2008 – and lost the nomination anyway. But this year’s result still gives the political universe pause. Romney, now seen as the moderate in the field, got swept by a movement conservative in a year when the Republican base is spoiling to take on President Obama with a clear choice, not what some call an echo.

And even though Romney enjoys a crushing lead against the rest of the GOP field in money and organization, at least one leading conservative is warning that Santorum can’t be written off – and that he’d better brace himself.

“Santorum has a chance,” William Kristol, editor of The Weekly Standard, wrote Tuesday night. “He's run an impressive campaign, but he’d better be wearing armor and kevlar tomorrow morning, when the Romney team unleashes all of its negative artillery against him.”

In the final days before Tuesday’s contests, the Romney campaign sensed trouble was brewing and began to go after Santorum’s record as a senator, including his support for “pork-barrel spending” – funding for special projects in his home state.

But Romney has a bigger Achilles’ heel: his reform of the Massachusetts health-care system from his days as governor, the template for Mr. Obama’s reform. “Repeal Obamacare” is one of the big rallying cries of 2012, and even though Romney says that’s his top priority, he still defends “Romneycare” as a state prerogative. Santorum has pounded hard on that issue.

There were no entrance polls on Tuesday to gauge voter motivations, but Mr. Kristol flags health care as a big factor. “I suspect at the heart of their concern was Romneycare,” he writes. “And I suspect it's worth Mitt Romney getting worried about.”

Not only does the central concern over health-care reform – the individual mandate to purchase insurance in both Massachusetts and nationally – mitigate Romney’s ability to attack Obama, but so, too, does the latest uproar over birth control. New federal rules requiring religious employers to offer birth control and sterilization in their health plans have inflamed sentiment among social conservatives, including some Roman Catholics, who account for a big swath of the electorate. “Romneycare” has a similar birth control provision.